共查询到20条相似文献,搜索用时 46 毫秒
1.
R. Golovchak O. Shpotyuk A. Kozdras B. J. Riley S. K. Sundaram J. S. McCloy 《Journal of Thermal Analysis and Calorimetry》2011,103(1):213-218
Radiation-induced physical aging effects are studied in binary As
x
S100−x
and As
x
Se100−x
(30 ≤ x ≤ 42) glasses by conventional differential scanning calorimetry (DSC) method. It is shown that γ-irradiation (Co60 source, ~3 MGy dose) of glassy As
x
S100−x
caused a measurable increase in glass transition temperature and endothermic peak area in the vicinity of glass transition
region, which was associated with acceleration of structural relaxation processes in these materials. In contrast to sulfide
glasses, the samples of As–Se family did not exhibit any significant changes in DSC curves after γ-irradiation. The observed
difference in radiation-induced physical aging between sulfides and selenides was explained by more effective destruction-polymerization
transformations and possible metastable defects formation in S-based glassy network. 相似文献
2.
The thermal denaturation of DNA and tRNAs was investigated by differential scanning calorimetry (DSC). Endothermic peaks were
observed in the DSC curves when the samples were heated. The denaturation temperatures (T
d) and denaturation enthalpies (ΔH
d) of samples of lyophilized powder and of samples in 4 mol/dm3 urea solution were obtained. The experimental results showed that the thermal stabilities of DNA and tRNAs were obviously
different under these conditions.
This research was supported by the National Science Foundation of China. 相似文献
3.
Joint results of the differential scanning calorimetry (DSC) and thermogravimetry (TG) experiments were the basis for the
fusion enthalpy and temperature determination of the biuret (NH2CO)2NH (synthesis by-product of the urea fertilizer (NH2)2CO). Recommended values are Δm
H = (26.1 ± 0.5) kJ mol−1, T
m = (473.8 ± 0.4) K. The DSC method allowed for the phase diagrams of “water–biuret,” “water–urea,” “urea–biuret” binary systems
to be studied; as a result, liquidus and solidus curves were precisely defined. Stoichiometry and decomposition temperature
of the biuret hydrate identified, composition of the compound in “urea–biuret” system was suggested. 相似文献
4.
M. R. Sovizi 《Journal of Thermal Analysis and Calorimetry》2010,102(1):285-289
Data on the thermal stability of drugs was required to obtain information for handling, storage, shelf life and usage. In
this study, the thermal stability of two nonsteroidal anti-inflammatory drugs (NSAIDs) was determined by differential scanning
calorimetry (DSC) and simultaneous thermogravimetery/differential thermal analysis (TG/DTA) techniques. The results of TG
analysis revealed that the main thermal degradation for the naproxen and celecoxib occurs in the temperature ranges of 196–300
and 245–359 °C, respectively. The TG/DTA analysis of compounds indicates that naproxen melts (at about 158.1 °C) before it
decomposes. However, the thermal decomposition of the celecoxib started about 185 °C after its melting. The influence of the
heating rate (5, 10, 15, and 20 °C min−1) on the DSC behavior of the both drug samples was verified. The results showed that, as the heating rate was increased, decomposition
temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor
for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E696 and Ozawa. Based on the
values of activation energy obtained by various methods, the following order for the thermal stability was noticed: naproxen
> celecoxib. Finally, the values of ΔS
#, ΔH
#, and ΔG
# of their decomposition reaction were calculated. 相似文献
5.
Douglas L. Cassimiro Clóvis A. Ribeiro Jorge M. V. Capela Marisa S. Crespi Marisa V. Capela 《Journal of Thermal Analysis and Calorimetry》2011,105(2):405-410
Meglumine, (2R,3R,4R,5S)-6-methylaminohexane-1,2,3,4,5-pentol, is a carbohydrate derived from sorbitol in which the hydroxyl group in position one
is replaced by a methylamine group. It forms binary adducts with substances having carboxyl groups, which have in common the
presence of hydrogen bonding as the main force in the stabilization of these species. During melting, adducts of meglumine
with flunixin (2-[[2-methyl-3-(trifluoromethyl)phenyl]amino]pyridine-3-carboxylic acid) polymerize or self-assemble in amorphous
supramolecular structures with molecular weights around 2.0 × 105 kDa. DSC curves, in a first heating, show isomorphic transitions where the last one at 137 °C for the flunixin-meglumine
adduct originated the supramolecular amorphous polymers with glass transition around 49.5 °C. The kinetic parameters for the
thermal decomposition step of the polymers were determined by the Capela-Ribeiro non-linear isoconversional method. From data
for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15, and 20 °C min−1, the E
α and B
α terms could be determined and, consequently, the pre-exponential factor, Aα, as well as the kinetic model, g(α). 相似文献
6.
Trilochan Swain 《Journal of Thermal Analysis and Calorimetry》2011,103(3):1111-1117
A new inorganically template metaphosphate of Co(II) complex has been synthesized and characterized by different measurements
such as DSC, FT-IR, C–H–N–O–S, ESR, TG-DTA and X-RD. Differential Scanning Calorimeter (DSC) elucidated negative specific
heat of the system and has used to evaluate some thermo dynamical constants like activation energy (E
a), frequency factor (A), enthalpy and entropy of that system. The specific heat capacity of the system is measured both in atmospheric O2 and N2 atmosphere at different heating rates of 278, 283, 293 and 298 K min−1 in room atmosphere and 288 K min−1 in N2 atmosphere. 相似文献
7.
Seyed Ghorban Hosseini Abbas Eslami 《Journal of Thermal Analysis and Calorimetry》2010,101(3):1111-1119
In order to investigate relative reactivity of different oxidants in solid-state reactions of pyrotechnic mixtures, thermal
properties of Sn + Sr(NO3)2, Sn + Ba(NO3)2, and Sn + KNO3 pyrotechnic systems have been studied by means of TG, DTA, and DSC methods and the results compared with those of pure oxidants.
The apparent activation energy (E), ΔG
#, ΔH
#, and ΔS
# of the combustion processes were obtained from the DSC experiments. The results showed that the nature of oxidant has a significant
effect on ignition temperature, and the kinetic of the pyrotechnic mixtures’ reactions, and the relative reactivity of these
mixtures was found to obey in the following order: Sn + Sr(NO3)2 > Sn + Ba(NO3)2 > Sn + KNO3. 相似文献
8.
Heating rate effect on the DSC kinetics of oil shales 总被引:1,自引:0,他引:1
M. V. Kök 《Journal of Thermal Analysis and Calorimetry》2007,90(3):817-821
This research was aimed to investigate the combustion and kinetics of oil shale samples (Mengen and Himmetoğlu) by differential
scanning calorimetry (DSC). Experiments were performed in air atmosphere up to 600°C at five different heating rates. The
DSC curves clearly demonstrate distinct reaction regions in the oil shale samples studied. Reaction intervals, peak and burn-out
temperatures of the oil shale samples are also determined. Arrhenius kinetic method was used to analyze the DSC data and it
was observed that the activation energies of the samples are varied in the range of 22.4–127.3 kJ mol−1 depending on the oil shale type and heating rate. 相似文献
9.
The use of olaquindox (OLA) as an additive in animal feedstuffs has been prohibited in the European Union and many other countries.
In this study, a highly sensitive and specific indirect competitive enzyme-linked immunosorbent assay (ELISA) for determination
of OLA in animal feed samples was developed. OLA was activated by N′N-carbonyldiimidazole and coupled with bovine serum albumin (BSA) and ovalbumin (OVA). It was found that the sensitivity and
specificity of the two antisera were very similar, with the IC50 values of 16 ng mL−1 and 19 ng mL−1, respectively. Cross-reactivity was less than 35% for four structurally related compounds and no recognition of five other
antibiotics was observed. The better antiserum I was selected for further experiments, for example testing stability, solvent
effect, accuracy, and precision. The IC50 value for eight standard curves was in the range 12–18 ng mL−1 and the LOD at a signal-to-noise ratio of 3 (S/N = 3) was 0.31 ± 0.11 ng mL−1. The ELISA tolerated 5% methanol without significant influence on IC50 value. The recoveries of spiked OLA in five different animal feed types including auxin, pig complex feed, fish complex feed,
broiler concentrated feed, and pig premix feed were in the range 88.3–119.0% and the intra-assay relative standard deviation
(RSD) was within 4.7–33.5% (n = 3). The ELISA for unspiked feed samples was confirmed by high-performance liquid chromatography (HPLC), with a high correlation
coefficient of 0.9862 (n = 5). The proposed ELISA could be a feasible quantitative/screening method for OLA analysis in feed samples with the properties
of high sensitivity, specificity, simplicity of sample pretreatment, high sample throughput, and low expense.
Figure Polyclonal antibody based ELISA for detection of olaquindox 相似文献
10.
Li Y Dong F Liu X Xu J Li J Lu C Wang Y Zheng Y 《Analytical and bioanalytical chemistry》2011,400(9):3097-3107
A rapid and simple miniaturized liquid–liquid extraction method has been developed for the determination of topramezone in
soil, corn, wheat, and water samples using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-electrospray
ionization (ESI)/MS/MS). The established method for the extraction and purification procedure was based on liquid–liquid partitioning
into an aqueous solution at a low pH (pH ≈ 2.5), followed by back-partitioning into water at pH > 9. Two precursor, product
ion transitions for topramezone were measured and evaluated to provide the maximum degree of confidence in the results. Under
negative ESI conditions, quantitation was achieved by monitoring the fragment at m/z = 334 and the qualitative fragment at m/z = 318, whereas also collecting the corresponding parent ion at m/z = 362. Chromatographic separation was achieved using gradient elution with a mobile phase consisting of methanol and a 0.01%
aqueous ammonium hydroxide solution. Recovery studies for soil, corn, wheat, and water were conducted at four different topramezone
concentrations (5 or 10, 50, 100, and 1,000 μg kg−1); the overall average recoveries ranged from 79.9% to 98.4% with intra-day relative standard deviations (RSD) of 3.1~8.7%
and inter-day RSD of 4.3~7.5%. Quantitative results were determined from calibration curves of topramezone standards containing
1–500 μg L−1 with an R
2 ≥ 0.9994. Method sensitivities expressed as limits of quantitation were typically 6, 8, 9, and 1 μg kg−1 in soil, corn, wheat, and water, respectively. The results of the method validation confirmed that this proposed method was
convenient and reliable for the determination of topramezone residues in soil, corn, wheat, and water. 相似文献
11.
The applicability of ATR-FTIR for the determination of the HDO content in heavy water (D2O) was investigated. Two groups of calibration standard solutions, of low contents (0–1 n% H2O in heavy water) and of higher contents (0–10 n% H2O in heavy water) were prepared by adding properly calculated amount of H2O to D2O by weight. The absorbances at 3400 cm−1 (ν, O–H) against the calibration standards were measured five times using two kinds of interchangeable IREs (1 bound and
9 bound reflections). And four calibration curves were obtained by linear least square fit of the measured absorbances for
the four different measurement conditions, which are (1) for low contents group using 1 bound reflection, (2) for low contents
group using 9 bound reflections, (3) for higher contents group using 1 bound reflection, (4) for higher contents group using
9 bound reflections. Determined contents (c
0) of each calibration standards for the four measurement conditions were obtained by the calibration curves and compared to
the calculated contents (c
cal). The uncertainty sources were considered when the HDO in heavy water is determined according to the procedure of this work.
The uncertainties u(c
0) of the determined contents (c
0) for the four different measurement conditions were calculated. 相似文献
12.
Brina Dojer Amalija Golobi? Zvonko Jagli?i? Matja? Kristl Miha Drofenik 《Monatshefte für Chemie / Chemical Monthly》2012,19(5):175-180
Abstract
A new coordination compound of zinc fluoride and hydroxylammonium, (NH3OH)2ZnF4, was obtained after dissolving zinc powder in hydrofluoric acid (40%) and adding solid hydroxylammonium fluoride. The colourless crystals were characterised chemically, magnetically, structurally by single-crystal X-ray diffraction analysis, and thermogravimetrically by TGA and DSC analysis. The structure consists of NH3OH+ cations and ZnF6 octahedra in which the metal ion lies on the inversion centre. Each of the ZnF6 octahedra shares four of its vertices in a way that each vertex is shared between two octahedra. Oxygen and nitrogen atoms of hydroxylammonium cations are donors of hydrogen bonds. Hydroxylamonium fluorozincate crystallizes monoclinic, P21/c, with cell parameters a = 8.1604(4) ?, b = 5.8406(3) ?, c = 5.6586(2) ? and β = 94.745(3)°. The compound decomposes above 373 K in four steps, obtaining ZnO as the final residue. Magnetic properties of the compound were studied between 2 and 300 K, giving the prevailing diamagnetic behaviour with room temperature susceptibility of −9 × 10−5 emu mol−1. 相似文献13.
Shashi B. Kalia Priyanka Sankhyan R. Puri J. Christopher 《Journal of Thermal Analysis and Calorimetry》2012,107(2):597-605
Non-isothermal techniques, i.e. thermogravimetry (TG) and differential scanning calorimetry (DSC), have been applied to investigate
the thermal behaviour of carbaryl (1-naphthyl-N-methylcarbamate = 1-Naph-N-Mecbm) and its complexes, M(1-Naph-N-Mecbm)4X2, where M = Cu, X = Cl, NO3 and CH3COO and M = Zn, X = Cl. Carbaryl and Zn(1-Naph-N-Mecbm)4Cl2 complex exhibit two-stage thermal decomposition while the copper(II) complexes exhibit three and four-stage decomposition
in their TG curves. The nature of the metal ion has been found to play highly influential role on the nature of thermal decomposition
products as well as energy of activation ‘E*’. The presence of different anions does not seem to alter the thermal decomposition patterns. The complexes display weak
to medium intensity exothermic and endothermic DSC curves, while the free ligand exhibits two endothermic peaks. The kinetic
and thermodynamic parameters namely, the energy of activation ‘E*’, the frequency factor ‘A’ and the entropy of activation ‘S*’ etc. have been rationalized in relation to the bonding aspect of the carbaryl ligand. The nature and chemical composition
of the residues of the decomposition steps have been studied by elemental analysis and FTIR data. 相似文献
14.
Liu X Xu J Li Y Dong F Li J Song W Zheng Y 《Analytical and bioanalytical chemistry》2011,399(7):2539-2547
A sensitive and effective method for simultaneous determination of triazolopyrimidine sulfonamide herbicide residues in soil,
water, and wheat was developed using ultra-performance liquid chromatography coupled with tandem mass spectrometry. The four
herbicides (pyroxsulam, flumetsulam, metosulam, and diclosulam) were cleaned up with an off-line C18 SPE cartridge and detected
by tandem mass spectrometry using an electrospray ionization source in positive mode (ESI+). The determination of the target
compounds was achieved in <2.0 min. The limits of detection were below 1 μg kg−1, while the limits of quantification did not exceed 3 μg kg−1 in different matrices. Quantitation was determined from calibration curves of standards containing 0.05–100 μg L−1 with r
2 > 0.997. Recovery studies were conducted at three spiked levels (0.2, 1, and 5 μg kg−1 for water; 5, 10, and 100 μg kg−1 for soil and wheat). The overall average recoveries for this method in water, soil, wheat plants, and seeds at three levels
ranged from 75.4% to 106.0%, with relative standard deviations in the range of 2.1–12.5% (n = 5) for all analytes. 相似文献
15.
Alexandra Ioiţescu Gabriela Vlase T. Vlase G. Ilia N. Doca 《Journal of Thermal Analysis and Calorimetry》2009,96(3):937-942
The synthesis of four types of hydroxyapatite synthesized from calcium chloride and four different organic phosphites is presented.
The method of synthesis chosen is the sol–gel route, which has a number of advantages compared to other methods, like the
intimate contact between reactants and the milder synthesis conditions. The samples were thermally treated, the TG/DTG/DTA
curves being obtained at four heating rates, namely: 7, 10, 12 and 15 °C min−1. The samples were characterized before and after the thermal treatment using FT-IR analysis. The FT-IR spectra certified
that the formed compounds represent hydroxyapatite. Based on the information from the TG curves and IR spectra interpretation,
a reaction mechanism was proposed. 相似文献
16.
M. Jafarzadeh I. A. Rahman C. S. Sipaut 《Journal of Sol-Gel Science and Technology》2009,50(3):328-336
A modified preparation of silica nanoparticles via sol–gel process was described. The ability to control the particle size
and distribution was found highly dependent on mixing modes of the reactants and drying techniques. The mixture of tetraethoxysilane
and ethanol followed by addition of water (Mode-A) produced monodispersed powder with an average particle size of 10.6 ± 1.40 nm
with a narrow size distribution. The freeze drying technique (FD) further improved the quality of powder. In addition, the
freeze dried samples have shown unique TGA decomposition steps which might be related to the well-defined structure of silica
nanoparticles as compared to the heat dried samples. DSC analysis showed that FD preserved the silica surface with low shrinkage
and generated remarkably well-order, narrow and bigger pore size and pore volume and also large endothermic enthalpies (ΔH
FD = −688 J g−1 vs. ΔH
HD = −617 J g−1) that lead to easy escape of physically adsorbed water from the pore at lower temperature. 相似文献
17.
Taís Vanessa Gabbay Alves Eraldo José Madureira Tavares Fauze Ahmad Aouada Charles Alberto Brito Negrão Marcos Enê Chaves Oliveira Anivaldo Pereira Duarte Júnior Carlos Emmerson Ferreira da Costa José Otávio Carréra Silva Júnior Roseane Maria Ribeiro Costa 《Journal of Thermal Analysis and Calorimetry》2011,106(3):717-724
This paper reports the thermal characterization of polyacrylamide-co-methylcellulose hydrogels and the constituent monomers (acrylamide and methylcellulose). Polymeric materials can be used
to produce hydrogels, which can be natural, synthetic, or a mixture. The hydrogels described here were obtained by free radical
polymerization, in the presence of N,N′-methylene-bis-acrylamide as a cross-linker agent. Four acrylamide concentrations were used for the synthesis of hydrogels:
3.6, 7.2, 14.7, and 21.7% (w/v). The materials so obtained were analyzed by TG, DTG, DSC, and FT-IR. The TG curves of acrylamide
and methylcellulose showed three mass loss events. In DSC curves, the acrylamide exhibited one melting peak at 84.5 °C, and
methylcellulose indicated one exothermic event. Nevertheless, acrylamide was considered more stable than methylcellulose.
The TG curves of the hydrogels exhibited three mass loss events, and on the DSC curves, three endothermic events were observed.
It was verified that the different acrylamide proportions influenced the thermic behavior of hydrogels, and that the authors
considered the 7.2% hydrogel a promising drug carrier system. The absorption bands were well defined, confirming the presence
of the functional groups in the samples. 相似文献
18.
S. Calvo J. Escribano M. G. Prolongo R. M. Masegosa C. Salom 《Journal of Thermal Analysis and Calorimetry》2011,103(1):195-203
The effect of a low profile additive, poly(ε-caprolactone) (PCL), on the thermal and mechanical properties of unsaturated
polyester resins (UP) was investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA),
and tensile tests. The morphology of the systems has been studied by scanning electronic microscopy (SEM). Two PCL molecular
mass were selected (PCL2: M
n = 2000 g mol−1 and PCL50: M
n = 50000 g mol−1) to analyze the influence of the molecular mass and the content of PCL on the UP resins and to establish the relation between
thermomechanical behavior and morphology. DSC and DMTA glass transition temperatures (T
g) of the UP cured samples containing PCL indicate that PCL2 is miscible with UP whereas for UP + PCL50 system, T
g values are very close to the ones corresponding to neat UP. Besides in UP + PCL2 systems, one phase morphology is observed
in which PCL2 would act as solvent of the reacting mixture along curing process; however, UP + PCL50 systems present phase-separated
morphology. The presence of PCL2 and PCL50 in UP resin leads to a decrease of the tensile strength and the Young′s modulus
as much notorious as the PCL concentration increases. For UP + PCL2 system the elongation at fracture increases in relation
to neat UP, increasing as well with the PCL content. 相似文献
19.
Gabriel Lima Barros de Araujo Dalva Lucia Araujo de Faria Márcio Henrique Zaim Flávio Machado de Souza Carvalho Fabio Ramos Dias de Andrade Jivaldo do Rosario Matos 《Journal of Thermal Analysis and Calorimetry》2010,102(1):233-241
Tibolone polymorphic forms I (monoclinic) and II (triclinic) have been prepared by recrystallization from acetone and toluene,
respectively, and characterized by different techniques sensitive to changes in solid state, such as polarized light microscopy,
X-ray powder diffractometry, thermal analysis (TG/DTG/DSC), and vibrational spectroscopy (FTIR and Raman microscopy). The
nonisothermal decomposition kinetics of the obtained polymorphs were studied using thermogravimetry. The activation energies
were calculated through the Ozawa’s method for the first step of decomposition, the triclinic form showed a lower E
a (91 kJ mol−1) than the monoclinic one (95 kJ mol−1). Furthermore, Raman microscopy and DSC at low heating rates were used to identify and follow the thermal decomposition of
the triclinic form, showing the existence of three thermal events before the first mass loss. 相似文献
20.
I. González-Mariño I. Rodríguez J. B. Quintana R. Cela 《Analytical and bioanalytical chemistry》2010,398(5):2289-2297
An expeditious method for the determination of triclosan (TCS) and methyl triclosan (MTCS) in sludge and sediment samples
is presented. Extraction and cleanup steps were integrated in the same process using matrix solid-phase dispersion as sample
preparation technique. Effects of different variables on the efficiency and the selectivity of the sample preparation process
are discussed. Under final working conditions, samples (0.5 g) were dispersed with diatomaceous earth (1 g) and transferred
to a polypropylene syringe containing 2 g of silica impregnated with sulphuric acid (15%, w:w). Analytes were recovered with 10 mL of dichloromethane. After solvent exchange to ethyl acetate, TCS was converted into
the tert-butyldimethylsilyl derivative, and the extract was analysed by gas chromatography-mass spectrometry, without any additional
cleanup. Obtained recoveries, for sludge and sediment samples spiked at different concentration levels, ranged from 86% to
113%, with associated standard deviations between 2 and 13%. Limits of quantification of the global method were 6 and 7 ng g−1 for MTCS and TCS, respectively. Both compounds were detected in all the processed sludge samples with maximum concentrations
of 191 ng g−1 (MTCS) and 2,640 ng g−1 (TCS). The parent bactericide was also found in some sediment samples at concentrations up to 200 ng g−1. 相似文献